Bedrock underlying the Alice Dams and Reservoirs consist of sandy silt of the Brule Formation. Project histories (USBR, 1912) allude to sand and gravel cover of about 3 meters at the damsite. There is no known record of the nature and thickness of material overlying the Brule Formation elsewhere at the site, it is likely that the valley bottom contains material of a thickness comparable to that at the damsite, and that the entire area is mantled by eolian sand and loess. While Brule is generally massive in the subsurface, it develops jointing when exposed to air. Water exploits these joints, forming fissures. There is no evidence of post-Miocene faulting at either Lake Alice or Minatare damsites or within 60 km of the sites. In addition, the smooth gentle slopes adjacent to the reservoirs suggest there are no active landslides at the site.